The present invention is directed on a composite glass and to a method for producing a coated plastic foil, thereby preferably to be used for such composite glass.
At first, some entities shall be defined:
Visible light range:
Spectral range between 380 nm and 780 nm.
Sunlight:
Spectral range between 200 nm and 2500 nm.
Near infrared:
Spectral range between 780 nm and 1200 nm.
Reflection coefficient R.sub.VIS :
With the spectral sensitivity to luminosity of the human eye weighted ratio of reflected and impinging light: ##EQU1##
wherein:
R(.lambda.) is the reflection value at a specific wavelength .lambda. PA1 V(.lambda.) is the spectral sensitivity to luminosity of the human eye PA1 S(.lambda.) is the spectral radiation distribution of standard light D65 (color temperature 6500K). PA1 T(.lambda.) Transmission value at a specific wave length .lambda., PA1 S.sub.S (.lambda.) spectral distribution of the sun radiation. PA1 A(.lambda.) the absorption value at a specific wave length .lambda.. PA1 Absorbing glass, e.g. "green glass": Green glass is a colored, absorbing glass which appears in the visible spectral range and in transmission greenish. A typical transmission course for light impinging perpendicularly and considered along the entire sun light spectral range is shown in FIG. 1 (solid line) altogether with the transmission course of the ideal glass (dashed line). In dependency of the concentration of coloring and of the thickness of the glass, the absorption may be increased or lowered, but the transmission varies in the visible spectral range too as the course remains qualitatively the same. PA1 Absorbing glass is limited with respect to its sun protection effect because it only acts via absorption, which and according to E.sub.SUN leads as well to heating up a room which is situated opposite to impinging sun radiation, as e.g. and especially to heating up of the interior room of a vehicle which is provided with such a sun protection system. Besides of that, the slope of the absorption edge between visible spectral range and near infrared spectral range is limited; if within the visible spectral range there is requested a minimal transmission, then the transmission in the near infrared spectral range may not be realized infinitely low. PA1 So-called D/M/D layer systems (dielectric layer/metal layer/dielectric layer) which are deposited either on glass substrates, as e.g. and especially on car window glass directly or on a foil, mostly on a polyester foil, which latter is subsequently embedded into a composite glass. Thereby, the plastic foil provided with the coating is typically assembled to a composite glass via a polyvinylbutyral-PVB-foil. As typical dielectric layer materials oxides of Zn, Ti, In etc. are used, as metal layer especially silver. PA1 U.S. Pat. No. 5,532,062: ZnO/Ag/ZnO; for improving resistance against surrounding Zn, ZnO respectively is doped (e.g. with Si, Ti, Cr, . . . ) PA1 U.S. Pat. No. 5,320,893: D/M/D; here a protection system is "sealed" by means of a specific glass compound technique and in thereby protected with respect to surrounding. PA1 U.S. Pat. No. 5,510,173: D/M/D; to increase resistance of a protective system with respect to the surrounding the system is modified to a D/M/DD (typically indium oxide/Ag/indium oxide/indium tin oxide) PA1 DE 30 27 356: D/M/D; to increase resistance with respect to the surrounding the dielectric layers of a protecting system are realized as metal oxide nitride compounds. PA1 with increasing thickness of the metal layer the absorption in the visible reflection-suppressed spectral range as well as the reflection in the infrared range rise. This leads to the fact that the metal layer thickness is not freely selectable, but must be tailored so that the transmission in the visible spectral range still reaches the requested value of e.g. 75%. If a higher transmission is to be reached in the visible spectral range, this automatically leads to a lower infrared reflection and thus to a lower sun protection effect. PA1 The suppression of reflection in the visible spectral range has a so-called "V characteristic", which means that the reflection is minimal at a specific wave length, risen significantly towards shorter and towards higher wave lengths. Because sensitivity of the human eye is maximum in the green spectral range the reflection minimum is realized in the green spectral range so as to be able to realize maximum metal layer thickness, which, on the other hand, leads to most efficient blocking of the near infrared. Thereby, there results necessarily a reflection which appears bluish/reddish, i.e. lilac. Every variation of the reflection color, which may be desired especially due to aesthetic aspects--relevant when looking at a window from the outside, because here a bright surrounding is reflected in the window, the background thereof--the inside of the car--being relatively dark--, may only be realized in deficiency of the protection effect with respect to near infrared radiation. Attention is lead on the U.S. Pat. No. 4,965,121 where a D/M/D system is proposed, the reflection color thereof being from neutral to bluish. According to the examples disclosed therein one may understand that there is a trade-off between color neutrality and sun radiation protection. PA1 Further, D/M/D systems are electrically conductive. This has the advantage that e.g. an electrically heatable window or a so-called "low emissivity" window or screen may be realized (low emission coefficient in the far infrared, so that the energy loss by heat radiation in the room temperature range is reduced). This nevertheless has the significant drawback that a window provided with a D/M/D system becomes impermeable to electromagnetic frequencies, which are necessary for operating infrared remote controls, radio, mobile phones, GPS etc. in the car or out of the car. Additionally, it is considerably more difficult to realize so-called "aerial windows", at which aerials or antennas are integrated into the composite window because by using a D/M/D system respective surface areas of the window must be masked out from coating or possibly at the compounding process, which leads to a considerable additional effort. PA1 at which the color appearance may be flexibly selected, especially at preferred embodiments, PA1 at which the coating is stable with respect to influences from surrounding, PA1 which, especially in a preferred form of realization, is low-cost in manufacturing and may be realized with flexibly variable coatings, PA1 which realizes with respect to sun protection an efficient separation of transmission in the visible spectral range and reflection in the near infrared spectral range, PA1 which especially in preferred embodiments maintains the advantages of foil-relayed systems with respect to glass systems (see below). PA1 800 nm.ltoreq..lambda..ltoreq.1100 nm, PA1 850 nm.ltoreq..lambda..ltoreq.1000 nm. PA1 n.sub.H.gtoreq.2.40, PA1 n.sub.H.gtoreq.2.55 PA1 n.sub.L.ltoreq.1.7, PA1 E.sub.SUN.ltoreq.60%. PA1 T.sub.VIS.gtoreq.75%. PA1 T.sub.SUN.ltoreq.50%. PA1 R.sub.SUN.gtoreq.23%.
Transmission coefficient T.sub.VIS :
With the spectral sensitivity to luminosity of the human eye weighted ratio between transmitted and impinging light: ##EQU2##
wherein there is further valid:
Transmission coefficient T.sub.SUN :
With the spectral radiation distribution of the sun weighted ratio of transmitted light and impinging light: ##EQU3##
wherein there is valid:
Reflection coefficient R.sub.SUN :
With spectral radiation distribution of the sun weighted ratio of reflected light and impinging light: ##EQU4##
Absorption A.sub.SUN : ##EQU5##
wherein there is valid:
Sun heat-up specification value. EQU E.sub.SUN =T.sub.SUN +A.sub.SUN /2
The smaller E.sub.SUN of a sun radiation protection system becomes the better is its protection ability.
The minimum value possible for E.sub.SUN for car windows is given by the fact that within the visible spectral range a minimum transmission is required, e.g. of 75% for front screens of cars according to ECE Standard No. 43. E.sub.min, SUN is defined by the so-called "ideal glass". It has within the visible spectral range a constant required transmission of e.g. 75% according to a constant absorption of 25% and further features in the ultraviolet spectral range (.lambda.&lt;380 nm) as well as in the infrared range (.lambda.&gt;780 nm) a constant reflection of 100%. Thereby, a maximum sun protection ability would be reached and simultaneously the standard of 75% transmission in the visible spectral range would be fulfilled.
Protection from sun radiation is realized today substantially by two approaches:
Thereby, it is known that silver is best suited to effectively separate light within the visible spectral range from light in the infrared spectral range. Due to its optical constants, namely refractive index n and extinction coefficient k, silver allows for a high transmission in the visible spectral range and for a high reflection in the near infrared spectral range. Attention is led thereabout on (1) H. A. Macleod, "Thin Film Optical Filter", Second Edition, Adam Hilger Ltd.; pp 292.
Equally known is nevertheless that silver is most sensitive to influences from the surrounding, as to humidity, formation of silver sulphide etc., and this irrespective whether such layer system is deposited on glass or on a plastic foil. Thereabout, attention is drawn to the following literature:
Characteristic for the behavior of a D/M/D system is that the requested transmission within the visible spectral range may only be reached by suppression of the reflection of the metallic layer. Thereabout, we again refer to (1). This is only possible for a narrow wave length range, and light which is transmitted through the D/M/D system is there significantly absorbed too. Thereby, especially the following two drawbacks result: